Aerodynamic braking of jet engine aircraft



July 12, 1960 v H. M. Fox 2,944,393

AERODYNAMIC BRAKING 0F JET ENGINE AIRCRAFT Filed April l5, 1955 INVENTOR. H.M. FOX

ATVTORNEY AERODYNAMIC BRAKING oF JET ENGINE f Homer M. Fox, Bartlesville, Okla., assigner to Phillips Petroleum Company, a corporation of Delaware i Filed. Apr. 15, 1955, Ser. No. 501,626

4 Claims. (Cl. 60-3554) This invention relates to aerodynamic braking of jet engine aircraft. In one of its more specicV aspects it relates to a method for produci-ng a reverse thrust in' a jet propelled aircraft at substantially constantcombustion level in said aircraft engine. In 'another of its more specic aspects this invention relates tomeans forrproviding aY reverse thrust 'to a jet propelled` aircraft with substantially no increase in back pressure upon the combustion chamber ofthe aircraft engine. In still'another of Vits more specicaspects itprovides ra means for providing a reverse thrust tov a jetpropelled' aircraft in greater magnitude than the vforward thrust developed..

Y The landing of vjetpropelled aircraft .presents aaprobl lem ,of increasing frather-j than. decreasing -diiiicultiels'with the development of thistype' f`of-,air'craft.'" While both-jet propelled yand propeller `lpropelled. aircraft.femployfwheel rakes for controlling theraircraft after-gialle.'initialy touch g down, the use of variable pitch propellersenables the pilot of a .propellerfpropelled ,aircraft t'ofrevers'e Ythe pitch of the propeller. so as to attain additional braking byrneans of the reverse thrust of the propeller. 'As jetpropelled aircraft are developed for higher ying speeds, 'it has been inevitable that such aircrafthave reqnireclrhigher landing speeds` due tothe decreased wing areaand they increased weight of the aircraft and variable pitch propel- 1ers are not available for braking purposes in jet propelled aircraft. One well known form of aircraft gas engine comprises a rotary compressor which is driven `by a turbinev so as to supply compressed air to a fuel combustion apparatus l n wherein motive fluid is generated by combustion ofl fuel and the products of combustion are expanded through the turbine and finally vdischarged*through` an exhaust" nozzle so asto develop vvajforward propellant thrust;l 'Y

Ordinarily, the landing of an aircraft employing a power plant of this type is eiected through a reduction i-n the forwardspeed of the aircraft rby reducing the ow ofsfu'e'l" to the combustion-chamber soV astoareduce thefdegree of combustion and the thrust andthisfreductionofsfuel ow also reduces the rotational speed of the compressor and turbine. A definite minimum mass flow throught'he" engine must, however, be maintained so as to'prevent'extinguishmentof the name in thef combustion "chamben The landing speed of a jet engine aircraftis usually very high and, with the present system of mechanically braking the wheels of the aircraft, extremely longV landing space is required in order to land the aircraft safely.

Several systems for landing 'gas' turbine :aircraft have been proposed whereby the speed of the aircraft is reduced on approaching.the landing surface and after touching down on the landing surface bymeans of directing a portion of the jet flow of exhaust gases forward inthe direction of flight so as to produce a rearward thrust on the aircraft. Although the development of this rearward thrustV or reversel thrust by the proposed' systems permits the aircraft to land in a somewhat shorter distance, the magnitude of thethrust directed rearward Vis often times insuicient for really eifective braking of I Patented .any t2, leso tering a wave-off signal.v This is very dilcult to d o withv Y the devices of the'prior art. Also, it is desirable in the Y plant substantially constant. g

It is an objectof this invention to provide a method for producing aV rearward thrust in a jet engine power plant at substantially constant combustion level in the combustion chamber and substantially constant rotational speed of the turbine and compressor.

It is an object of this invention to providean apparatus for producing a rearward thrust in a jetl engine power plant at substantially constant level ofV combustion `in the combustion chamber and substantially constant rotational speed of the turbine and compressor.`

lIt is another object of this invention to provide ajet engine power plant which permits an aircraft to'be landed celeration to maintain Vthe state of operation of the power It is st ill another objectief Vthis `ljet engine powerlplantinwhichf forwardthrfustfof-"the engine. i' k y The .provision of an apparatusywhich n n positive-in theregulationV in :the .forwardthrustjof a jet propelled 'aircraft isfstillA another object of'this'V invention." 4CStillfurtherfobjects and-advantagesfwill `be=lapplar`ent tof one skilled in the art upon "study of this-disclosure'includf ing the kdrawing wherein:` Y u i A schematic illus'tration of an vention is presented; n j flhe'present'` invention provides a method and apparatus in lan'aircraft for regulating the forward thrust produced by va turbojet power plant and for supplying a` rearwardly directed'thrst from the power plant withoutY interfering withthe state of operation of thepower plant. B-roadly,VV

' theV present invention `provides 'a means foi-directing a thrust rearwardly to induce .a braking action on the air# craft Withoutxaifecting the; level Vofcombustion inthe combustion V chamberl or the rotational` speed of thecom;

einbci'diment'` of this inmaintains the "power Vplant in a state.;ofoperation-which is Vreadily responsiveto; a possible demandfor a rapid yincreas'egin lforward;thrusts VThe magnitude ofthe' rear` wardly and'forwardlyrdirecting thrustsdeveloped `in the power.4v plantV of thisginvention can" be controlled' through'- out ia Wide range 'of values-and a rearward thrust exceed ing the `magnitude of Ythe Ynormal forward. thrustzkcan 'also t berobtained. The apparatusv ofA .this invention accom plishestheg-.controlf ofv the magnitude and the ,directionfof the thrust developed in the power plant in a simple and positive manner. f f `The present invention'provides a means for` bathing or reducing the elfective areaA of the-'rearwardly directing exhaust nozzle,l a AmeansV forrdirecting a portion or alll of the combustionl gas discharged from the turbine forward 'i wardthrust developed. "V'

manuevering of aircraft by rapid acceleration and deinfa shortened landing distancel andwhich increases the t male and' pressorandturbinef Thus,themethodofthisinvention'jy More specically, this apparatus provides an exhaust duct which is communicative with the rearwardly directing exhaust nozzle of the power plant and which is open to the atmosphere, or can be opened to the atmosphere, in a forward direction to develop a Yrearward thrust through the discharge of exhaust gases diverted from the turbine exhaust system. The flow of gases into this forwardly directing exhaust duct is regulated by a control means,rsuch as a control valve, located at thejunction of the forwardly directing exhaust duct with the Vrearwardly directing exhaust Vduct in a manner not to affect the aerodynamic flow within the system. The means provided to baille or reduce the 'eifectivearea 'of the rearwardly directing exhaust nozzle may comprise a variable area exhaust nozzle or any other means known in the art. Ordinarily, this battling means will only reduce-the discharge of combustion gases from the rearwardly directing exhaust nozzle instead 'of completely stopping the discharge of these gases to reduce the forward thrust of the power plant. The degree ofopening of this variable area nozzle is regulated in accordance with the position of `the control valve governing the flow of exhaust gases intoV the forwardly directing exhaust duct in order to maintain the turbine discharge pressure substantially constant and thereby not affect the rotational speed of the turbine and compressor. The rearwardly Vdirecting thrust developed by the discharge of exhaust produced from the forwardly directing duct is augmented by the combustion of additional fuel within the forwardly directing duct so that afrearward thrust :greater in magnitude than the forward thrustcanbeobtained whenit is desired. The aug-Y mentation of the'rearward thrust-.is accomplished by the combustion of fuel injected into the forwardly directing duct as in the conventional afterburner combustion system well known in the art.` The rearward thrust :developed is not augmented in V1all operations ofthe .power Yplant because the rearward'thrust obtained by diverting aportion of the combustion gases'from theturbine exhaust system and discharging this gas from the power plant in a forward direction is suiiicient in some opera tions. Ordinarily, the liow of fuel through the principal combustion chamber of the power plant is not changed when rearward thrust isdeveloped.

' As an example of the operation of my invention, reference is made to the drawing wherein oner embodiment of this invention is illustrated in a diagrammatic drawing, partly in section. The turboje't engine comprises an'outer casing Vstructure 10 having an inlet end 11 andan exhaust nozzle 12 located 'at the opposite end. Mounted within the casing 10 along the longitudinalaxis thereof 'is Van axial ow compressor 13,Y annular fuelt combustionapl paratus V14 and a turbine 15, the 'rotor Vof which is operativelyconnected to'the rotor of the compressor 13 by means of a shaft 16. .Fuel is suppliedY to combustion `ap`-V paratus`14 by line r17 and nozzle 18. Control'ofY the effective area of exhaust nozzle 12 is provided bymova'bl bafiie plate 19 which is rotatably mounted on outer casing 10 by pins 20. The casing structure -ltlis adapted to be mounted on or in the fuselage or wings of the aircraft vil'tll; the intake opening 1i pointed in the'direction of The forwardly directing duct of thisinvention comprisesfcylindrial casing 21, which has a discharge nozzle 22at oneend and is attached at the other end to the turbine'discharge zone 23 of the engine 'through opening 24in'c'asing 10 byfcylindrical section25. Casing 21 is arranged with discharge'noz'zle 22'poin'ted in the direction of night of the aircraft and is-preferably'located adjacent the'engine, as shown in the draw-ing, but can be located atf'adistance from the engine if so desired. Fuel issupplied tothe forwardly directingV casing 21 by fu'el line 26 andfuel-nozzles-27, located in casing 21 upstream from flame Vholder'23. The now ofexhausttgas from the turbine dischargepzonegZS of the turbojet engine is controlled `by butterfly valve 2.9. The movement of baiesn19`f-and able thrust.

buttery valve 29 is Vinterrelated in such a manner that the elfective area available for discharge of the combustion gas from the turbine discharge zone 23 remains substantially constant in all positions attained by -baiiies 19 and buttery valve 29. This control can be advantageously effected hydraulically by movement of piston 30` in pressure cylinder 31 so` as t'o'transmit Ya force to pressure cylinders 32i and 33. The force transmitted `to ,pressure cylinder 33 acts upon the opposed pistons within cylinder 33 so as to ratate bafes 19 through the movement of racks 34'and gear segments Y35 which are rigidly attached to baffles 19 on the opposite side from pins Z0' movably mounting bafes 19 onto casing 10. The force transmitted Vto pressure cylinder 32 also acts against a pis'- Vton mounted therein so as to rotate butterfly valve 29 through the action of rack 36 and gear segment 37. Pis ton 30 can be caused to reciprocate within cylinder 31.' through means of rack 37 and pinion 38 operated by motor 39. Motor 39 is areversible motor and is operated, by a manual switch (not shown).

A tail cone 40 is advantageously positioned in dischargey nozzle 22.

The forwardly directed duct Z1 is operated as lan afterburner by opening valve 41 in fuel line 26 so as to admit fuel to nozzles 27 andignite the added fuel by ignition. means 43. Ignition means 4Z'and 43 can he a spark'plu'g, a heated wire, a pilot flame, a powder charge'or other known ignition means.

Better understanding of the inventionmay result frorn the following descriptive example of theop'eration ofthe embodiment illustrated in the .,drawing. In anormal operation -ofthe turbojet engine,fsuch as in levellflight of the aircraft utilizing the braking systemof thisinvention,

the bafes 19 are in fully open position and .butterfly valve 29 substantially'completely closes 'opening 2d.l yNo fuel is supplied to fuel nozzles 27 Vin forwardly 'directing duct 21. Y 2 Y When it is desired to utilize tne braking system, `such as in landing the aircraft, the operator manipulates -the switch governing motor 39 so as to close baffles 19-and correspondingly'to -`open butterfly valve 29 the amount required to provide the desired amountof braking. `vWhen the maximum amount of braking is required, motor-39 is caused to substantially completely close haines 4@and to substantially open butterfly 'valve 29.' Thevoperator l also opens manually controlled vaive al' so as to introducebraking duct. The operator can, for exampledivertfthe flow-of exhaust gases so that'60` percent of the `thrust -is forwardand 40 percent of the thrust is rearward -so Vthat there is a net' forward thrust of 20 percent of the avail- Y Auxiliary fuel is then introduced into the braking duct and ignitedso as to 'provide additionalV rearward thrust. The amount of braking can be varied-'and controlled by simply varying the VVflow of fuel tothe braking duct. Ordinarily, the flow offuel to the combustion chamber of the engine will `notbe varied duringV the braking operation.

. Thus, I have provided means for braking ajet Apropelled aircraft which does not depend upon a delicate balance of diversion of ow of combustionV productsv from the engine combustion chamber for rearward thrust but instead provides a separate source yof combustionzproducts for the braking that is required.

Reasonable variations and modifications are possible within the scope of the disclosure of the present invention, the essence of which* is the provision of means to provide a reverse thrust to a turboiet engine '.by diverting.l at least V part-:of the turbine `,discharge ltofa forwardly directed Y l. A device for producing a reverse thrust at a substantially constant level of combustion to a continuous f combustion power plant, wherein fuel is burned in a comA bustion chamber and the products of combustion are expelled through a reaction noule so as to provide'thrust, which comprises auxiliary nozzle means positioned substantially parallel with and opposite to said reaction nozzle; conduit means communicating between said auxiliary nozzle and the interior of said power plant-intermediate the combustion` chamber and the reaction nozzle; first valve means positioned in said conduit means which closes said conduit means; fuel introducing means positioned in said conduit downstream from said lirst valve; second valve means operatively connected to said reaction nozzle which reduces the effective area-of said reaction nozzle; valve control means operativelyconnected to said first and second valve means so as to open said first valve `and to reduce the effective area of saidsecond valve simultaneously so that the effective area available for discharge of combustion gas from thev combustion chamber is maintained substantially constant whereby the pressure in ltheV combustion chamber is maintained vsubstantially `constant and the thrust of the power plant is reversed; and 'fuel ignition means positioned said conduit. v

.2. In a turbojet aircraft engine comprising acompres-V sor, combustion' chamber, turbine andjexhau'st i nozzle, and aerodynamic braking device comprising a braking nozzle positioned substantially parallel lwith'and opposite tosaid exhaustnozzle; a conduit connecting*` area available for discharge of combustion gas from the combustion chamber substantially Vconstant Yand tol divert the exhaust gases from'one nozzle to another Yati substantially constant exhaust gas pressure.

, in said conduit downstream from said fuel nozzles; means which ignites 'said fuel downstream lfrom said flame rholdenwalve meansV positioned in said `conduit adjacent said turbine discharge section;'closure means associated,l

sor, combustion chamber, turbine, turbine discharge section and exhaust nozzle, the improvement comprising a braking nozzle positioned substantially parallel with and opposite to said 'exhaust nozzle and havin-g a crosssectional area at least as large as that of the exhaust nozzle; a conduit of greater cross-sectional area than said braking nozzle operatively connecting the turbine discharge section with said braking nozzle; valve means in `said conduit which closes said conduit to said turbine discharge section; closure means associated with said exhaust nozzle which closes said nozzle; means which closes said closure means and opens -said valve simultaneously so that the cross-sectional area of the path of the gases from the turbine to the atmosphere is substantially constant; kmeans which introduces fuel to said conduit; and means for igniting fuel in said conduit.

4. In a turbojet aircraft engine comprising a compressor, combustion chamber, turbine, turbine discharge section and exhaust nozzle, the improvement comprising a .braking nozzle positioned substantially parallel with and opposite to said exhaust nozzle; a conduit of great cross sectional area than said 'braking nozzle operatively connecting said turbine discharge section with said braking nozzle; a tail cone positioned in said braking nozzle; a

v plurality of fuel nozzles positionedin saidY conduit so as to direct fuel'to'war'd said braking nozzle; a ameholder with said exhaust nozzle which closes said nozzle; and

vmeans Ywhich vcloses saidclosure means and opens said'A :valve simultaneously so thatvthe total effective crosssecetional areaof the exhaust nozzle and braking nozzle 3. In a turbojet aircraft engine comprising a eompresf e is maintained substantially constant.V

References Cited in the le of this patent UNITED STATES PATENTS Great Britain June 22, 1955 UNITED STATES PATENT oEEICE CERTIFICATE OF CORRECTION Patent No. 2,944,393 July l2, 1960 Homer M. Fox

It is hereby certified that error appears in the printed specification of the' above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 3ll for l"and" read an line 40f after "nozzle" insert which reduces lthe effective area of said exhaust nozzle line 4l,v strike out :"nozzle which reduces the effective area of said exhaust/'W column 6, line 2l, for "great" read greater line 341 for "Soe-tional" read sectional Signed and sealed this 31st day of January 1961.

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSN Attesting Oicer Commissioner of Patents 

